The North Pacific Gyre Oscillation and East Asian summer precipitation

This study examines the links between the North Pacific Gyre Oscillation (NPGO) and the East Asia (EA) summer precipitation (EASP) at a decadal scale. Maximum covariance analysis reveals that NPGO is the third mode regulating the decadal variation of EASP. 'Global warming' and Pacific Decadal Oscillation are the first two leading modes. Associated with NPGO, EASP exhibits a north-to-south '+-+' tripole pattern. The related atmospheric circulations are also examined. Results demonstrate that the linkage between NPGO and EA involves two processes, namely, extratropical and tropical processes. In the extratropical process, NPGO features an eastward propagating Rossby wave over the extratropical regions; this wave intensifies and displaces the EA jet stream northward. In the tropical process, NPGO is associated with a meridional circulation over the northeastern Pacific and an anomalous Walker circulation over the tropical oceans. The anomalous Walker circulation exhibits a downward branch over the western tropical Pacific and features low-level northerly wind over EA and western North Pacific region. The two processes strengthen the EA summer monsoon circulation and enhance the moisture transportation from oceans to northern EA; thus, the precipitation in the northern EA region increases and the precipitation in the central region decreases.